The present embodiments relates to a torque transmission device having variably adjustable stiffness, to an actuator having the torque transmission device, and to a robot.
Robots are being used more and more in direct contact with humans whether in patient care or in industry. Common to these applications is that an increased demand is made on the safety of robots. Thus, a human being injured by a robot if he is accidentally struck by a moving robot part is to be ruled out. In the event of faults (e.g., in the area of wearable robotics), a human joint being acted upon with too much force and as a result being injured also is to be ruled out. A known approach to this problem is the use of actuators with variable stiffness.
A high degree of mechanical stiffness is desired for achieving high levels of positioning accuracy. However, if a robot part is to be moved rapidly, or if the movement of a human joint is to be matched, a flexible mechanism and consequently a low degree of stiffness is desirable for achieving a high level of safety. Two approaches are known for realizing actuators with variable stiffness (e.g., variable stiffness actuator (VSA)).
Actuators with a high degree of stiffness are supplemented by a force or torque sensor. Using a suitable controller, this makes it possible to simulate a stiffness that is below the mechanical one. The force sensor, in this case, measures the force existing at the actuator or the existing torque. In dependence on the torque, the excursion is adjusted such that a mechanical spring is simulated.
The excursion is adjusted in proportion to the existing torque. The proportionality factor corresponds to the virtual stiffness. A disadvantage of the approach is the lack of intrinsic safety as in the event of a fault (e.g., failure of the force sensor or the) the intrinsic high degree of stiffness of the actuator comes into play.
The second approach is the structure of actuators, the stiffness of which is realized so as to be modifiable in a purely mechanical manner. In this case, a lever system with a variable force application is used. An actuator is connected for this purpose, for example, by an additional mechanical element that includes a spring as a central mechanism. In order to vary the stiffness of the spring, the lever arm of the force application is adjustable, for example, by an electric motor. A disadvantage of the approach is the relatively large amount of space required for the structure.